1. Field of the Invention
The present invention relates to an image pickup optical lens assembly, and more particularly to a low-priced optical lens assembly comprised of five lens elements that constitute the total length of the optical lens assembly and applied to an electronic product.
2. Description of the Related Art
As science and technology advance, the development of electronic products such as digital cameras, web cameras or mobile phone cameras tends to have a compact design to meet the user requirements for an optical lens assembly with good aberration correction ability, high resolution, and high image quality.
In general, a conventional optical lens assembly of a mini electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. If the image quality is taken into consideration, the optical lens assemblies with the four-lens and five-lens designs have advantages on aberration correction and modulation transfer function (MTF), and the five-lens design having a higher resolution than the four-lens design is applicable for electronic products of high video quality or high pixel requirement.
In various mini five-lens designs of an image pickup optical system with a fixed focal length, different combinations of positive and negative refractive powers are adopted. As disclosed in Japanese Pat. Publication Nos. JP2006-293042 and JP2005-266771, U.S. Pat. Publication Nos. US2004/0196571 and US2003/0117722, and R.O.C. Pat. No. TW M313781 adopt two sets of cemented doublet lenses to shorten the focal length of the optical system, but the two adjacent optical surfaces must adopt the same curvature and incurs a high level of difficulty for the optical design or aberration correction, and thus the application is very limited.
In small products such as digital camera, web camera, and mobile phone camera, the optical lens assembly requires a compact design, a short focal length and a good aberration correction. For different designs of the image pickup optical systems with a fixed focal length and five lens elements, a better aberration correction and an appropriate total length can be achieved by designing the fourth and fifth lens elements with different refractive powers. In particular, the optical system with a five-lens structure can meet the high pixel requirement, as disclosed in R.O.C. Pat. Nos. TW I329755, TW201038966 and TWM332199 and U.S. Pat. No. 7,710,665, and such optical systems tend to have a good aberration correction, but the total length of the optical systems still cannot meet the application requirements of a small electronic device. In a design adopting the fifth lens element with an inflection point and a shorter focal length as disclosed in U.S. Pat. No. 7,826,151, US2010/0254029, and US2010/0253829. The prior art adopts the fifth lens element with an inflection point to correct aberration or distortion. However, it is necessary to have a greater distance between the third lens element and the fourth lens element, which is unfavorable to the design for a shorter total length; or for the purpose of achieving a shorter total length, the distance between the fourth lens element and the fifth lens element is shortened too short, where the aberration correction will be difficult. Therefore, the present invention provides a feasible design to shorten the optical lens assembly, while using the refractive power of the five lens elements and the combination of convex and concave surfaces to improve the image quality for the application on compact electronic devices, in addition to the effect of reducing the total length of the optical lens assembly.